Numerous items such as smart phones, smart watches, tablets, automobiles, aerial drones, appliances, aircraft, exercise aids, and game controllers may utilize motion sensors during their operation. In many applications, various types of motion sensors such as accelerometers and gyroscopes may be analyzed independently or together in order to determine varied information for particular applications. For example, gyroscopes and accelerometers may be used in gaming applications (e.g., smart phones or game controllers) to capture complex movements by a user, drones and other aircraft may determine orientation based on gyroscope measurements (e.g., roll, pitch, and yaw), and vehicles may utilize measurements for determining direction (e.g., for dead reckoning) and safety (e.g., to recognizing skid or roll-over conditions).
Motion sensors such as accelerometers and gyroscopes may be manufactured as microelectromechanical (MEMS) sensors that are fabricated using semiconductor manufacturing techniques. A MEMS sensor may include movable masses that can respond to forces such as linear acceleration (e.g., for MEMS accelerometers) and angular velocity (e.g., for MEMS gyroscopes). The operation of these forces on the movable masses may be measured based on the movement of the masses in response to the forces. In some implementations, this movement is measured based on distance between the movable masses and sense electrodes, based on the variation of a capacitance formed by each movable mass and its respective electrode.
The movable masses of an exemplary MEMS accelerometer may include one or more suspended masses that deflect in response to linear acceleration. The components of the MEMS accelerometer may be sealed in order to prevent contamination of the environment of the MEMS accelerometer by outside contaminants such as moisture. Such contaminants may affect the operation (e.g., the movement of the movable masses in response to linear acceleration) or otherwise damage components of the MEMS accelerometer. If the seal of the MEMS accelerometer is broken, the contaminants may enter the cavity and the accelerometer may fail. The seal of the MEMS accelerometer may also maintain a pressure that is sufficient to provide damping for the movable masses of the accelerometer.
A MEMS gyroscope may also operate within a sealed environment. MEMS gyroscopes require one or more of the movable masses to be driven at a high frequency, and the operational characteristics of the gyroscope (e.g., a “quality factor” or “q-factor”) may depend up on the environment in which the gyroscope is operating. For example, the q-factor may change based on temperature and may be highly pressure dependent. Many MEMS gyroscopes may need a low pressure such as a high vacuum environment to operate normally. An increase in pressure may result in the lowering of the q-factor.